analisi dinamica

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    • Out-of-Plane Seismic Response of Masonry Façades Some Comparisons Among Full Dynamic and Pushover Analysis

    Siro Casolo, Giuseppina Uva

    Within the framework of the seismic risk assessment of monumental masonry buildings, we focus on the analysis of out–of–plane mechanisms which actually represent the most recurrent collapse mode for the façade of churches or basilicas. A full non-linear dynamic analysis is performed by adopting a rigid body and spring model (RBSM), where damage is entirely ascribed to the out-of-plane flexural behaviour. A phenomenological description of the cyclic response of the masonry material is provided in the definition of the constitutive prescriptions, including plastic energy dissipation and mechanical damage. Then, a comparison is made with a non-linear static pushover analysis, which is performed by means of the same RBSM under quasi-static loading, incrementally applied. The generalized force–displacement curve and the ultimate limit displacement capacity are evaluated, comparing them with the seismic displacement demand. As a case study, the church of Rosario in Guastalla was chosen, that was damaged by the Emilia Romagna Earthquake in 1987. A number of analyses have been performed, by adopting artificially generated accelerograms with different destroying potential, in order to investigate the correlation between the damage indicators obtained with the two procedures. The two methodologies showed a good agreement in the evaluation of the seismic response for low-medium seismic demands, even if NSPs tends to overestimate the damage, especially for high seismic levels.

    For this paper is available an extended abstract after the text in Italian

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    • Lo studio di interventi antisismici tramite analisi dinamiche con un modello ad elementi rigidi: il caso del Castello Maniace

    Siro Casolo, Vincenzo Petrini, Carlo Alberto Sanjust

    A specific numerical model is proposed for the in-plane dynamical analysis of a masonry monument, with particular attention to the design of interventions for seismic protection. In order to perform effective compu- tational analyses, the present model is conceived to operate at the macro-scale considering the energy dissipation capacity of the masonry material, as well as the effects of the masonry texture on the local damage mechanisms. In particular, the model was implemented according with a mechanistic point of view, in the spirit of the rigid body and spring model approach, RBSM. In the present application we describe the passage from the global three dimensional model of the Maniace Castle in Syracusae to the identification of the specific collapse mechanism that is more at risk, and that can be specifically described by means of a plane model. Then, the dynamics of a transversal cross-section of the hypostyle salon of the Castle is investigated with particular attention to the enhancement of the seismic response that can be achieved by an intervention of rebuilding and reshaping of the buttresses.

    This paper is available in Italian only.

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    • Analisi sismica di edifici esistenti in muratura con metodo dinamico: applicazione a Villa Faule (SI)

    Maria Luisa Del Savio, Luciano Galano

    In this paper a general method is given to evaluate the collapse seismic load of existing masonry buildings. The method is based on numerical analyses in which both linear and nonlinear models are used to evaluate the seismic response of the masonry assemblage. The structure is first idealized by a F.E. model to investigate the stress patterns produced by the static loads, then a simplified nonlinear dynamic model is used to predict the collapse seismic load. In addition, the F.E. model is useful to identify some mechanical parameters of the masonry and to establish the accuracy of the simplified approach. To this aim the first two modal shapes of the building are used. To exemplify the general methodology here discussed an application is presented for Villa Faule, to be found in the Tuscany countryside in the neighborhood of Colle di Val d’Elsa (Siena). The Villa Faule was built at the end of XVIII century and is representative of many similar country houses located in the same geographic zone. Considering the dilapidated state of the walls, of the timber floor slabs and of other architectural elements, in recent times a design was approved to strengthen and to rehabilitate the building. The subject of this study is the strengthened building because the large-scale numerical models are more reliable for such types of structures. The results showed that both the procedures were useful to investigate the structural problem. The F.E. model furnished a good prediction of the masonry stresses under vertical loads and predicted the modal shapes of the structure; at the same time it revealed that the simplified model was accurate. The nonlinear simplified method gave a prediction of the seismic ground acceleration intensity to be applied to achieve the building collapse. To this purpose the structure was subjected to the N-S acceleration record of El-Centro (Imperial Valley’s earthquake, 1940). The results showed that the value of the collapse peak ground acceleration was equal or more than 2.75 m/s2.

    This paper is available in Italian only.

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    • Influenza delle Tamponature sulla statica dei telai in c.a. in zona sismica

    Dora Foti, Massimiliano Borgia

    This paper describes a model able to evaluate the effect of masonry panels on reinforced concrete frames subjected to a seismic action. The panel is modelled as an equivalent diagonal element with a bilinear constitutive relation. The efficacy of the model is verified with an hysteretic model which considers some fundamental characteristics of masonry subjected to a seismic action (transitory phase between elastic and elasto-plastic behaviour, stiffness and strength decay, reduction of the hysteresis cycles due to the opening and closing of the cracks). This study shows that the presence of masonry panels causes a different distribution of the seismic action that usually concentrates in the lower floors (with accumulation of the damage in these levels) and the whole structure keeps in the elastic field.

    This paper is available in Italian only.